GCSE Chemistry: Rates of Reaction Guide

What affects rate of reaction

Reaction rate increases with higher temperature, higher concentration (or pressure for gases), smaller particle size (larger surface area) and the presence of a catalyst.

Collision theory

For a reaction to happen, particles must collide with enough energy (the activation energy). Increasing temperature or concentration increases the frequency and energy of collisions, speeding up the reaction.

Catalysts

A catalyst speeds up a reaction by providing an alternative pathway with a lower activation energy, without being used up itself in the reaction.

Measuring rate of reaction

Rate can be measured by tracking how quickly a reactant is used up or a product is formed, e.g. measuring the volume of gas produced over time, or the time taken for a solution to turn cloudy.

Common mistakes

• Forgetting a catalyst is not used up and doesn't appear in the balanced equation.
• Confusing surface area (smaller pieces = larger surface area = faster reaction) with particle size directly.
• Describing a graph's shape without linking it to what's happening to the reactant concentration over time.